yannigan, n. — Green’s Dictionary of Slang

yannigan n.

[baseball j. a rookie, a player not on the regular team]

(US und.) a fool, a newcomer.

1915		S. Ford Shorty McCabe on the Job (2007) 10: Well, post me for a Bush League yannigan if it don’t listen that way.
1991		B. McCarthy Vice Cop 267: The argot of the Gang [...] Loogins, yannigens—newcomers, second teams, bumpkin.